1. Field of the Invention
This invention relates generally to a wireless location system, more specifically, to a wireless Real Time Location System (RTLS) which uses audile and/or visible signals to exactly locate a unit being tracked or located (e.g. wireless tag) in an area.
2. Background of the Invention
Determining the location of assets, such as equipment, vehicles, inventory, etc., can be important in a variety of different applications. For example, large manufacturing companies typically have warehouses which are used to store parts and inventory. It is important to accurately and timely locate parts and inventory in order to timely and successfully manufacture products. One way to track the location of assets is to use a real time location system. A real time location system will associate each asset, or group of assets, with a tag device. The tag device is capable of communicating with a controller through one or more receivers to provide information used to determine the location of the tag device and thus the location of the associated asset.
A variety of methods may be used to determine the location of the tag device. One method is by signal strength or Received Signal Strength Indication (RSSI). In this method, the tag device may send a radio frequency signal that is received by one or more antennas that communicate with a controller. Based on the signal, the controller may determine where the tag device is located. This method is generally poor in terms of accuracy and reliability, as the path loss is highly dependent on environmental conditions and affected by fading due to multi path propagation. The accuracy of the RSII method declines rapidly as either the size of the covered area increases, or the size and quantity of metal or other RF reflecting objects and surfaces in and near the covered air space increases. In indoor environments, the reliability of this method is highly dependent on the wall materials and the level of RF signal attenuation between adjacent areas.
Another method to determine the location of the tag device is to determine a time difference of arrival of a tag device signal. In this method, a tag device will encode a time stamp on a signal that is transmitted. Each controller will report on when the tag device signal is received. While this method does work, it is generally not accurate when the distance between the tag device and the controller is small. The clock devices for each tag device and controller also need to be synchronized in order to provide accurate locations. Furthermore, this method, while giving a general location of the tag device, will not provide an exact location.
Presently, all current location systems only provide location data and perhaps a display (i.e., map) in order to try and find the item being sought. Thus, the problem with present real time location systems is making the systems sufficiently accurate so that someone with the location data provided by the location system can walk right to the item being sought.
Therefore, a need exists for a system and method that overcomes the problems associated with the prior art. The system and method will provide a wireless real time location system that is sufficiently accurate so that someone with the location data provided by the location system and the proper tools can walk right to the item being sought.